Honey Testing

In 2010, six shipments of high bioactive manuka honey worth about $6 million failed border tests, and threatened to close market access into the United States and China.

The honey was genuine, but the false-positive test results led to overseas agencies assuming this was because of sugar adulteration, which results in automatic disqualification by importing countries.

An investigation by scientist Karyne Rogers has shown that international laboratory tests designed to pick up adulterated honey were returning “false positives” on NZ manuka honey exports.

Honey exports are estimated to be worth in excess of NZ$110M annually and manuka honey accounts for at around 70% of that.

Any hint that honey has been adulterated is a disaster for exporters. Honey can be adulterated most commonly using cane sugar or corn syrup in a practice called stretching. Since 2010 there has been an increase in honey adulteration, especially in Asia, and now markets are increasingly vigilant in testing honey as it arrives.

An investigation by New Zealand scientist Karyne Rogers has shown that the internationally accepted laboratory test designed to detect cane sugar adulteration of honey was often giving false-positive results and causing problems for manuka honey in overseas markets. The test is called the AOAC C4 sugar test. Most overseas importers use the test on honey before purchase. This testing is usually conducted by the importer in European laboratories.

A failed sugar test results in loss of sales, which reduces a high quality export shipment into a more modest, lower quality domestic product, and affects future brand confidence and reputation.

Karyne Rogers has developed a modified procedure to give more accurate and reliable results for manuka honey. She says manuka honey’s unique properties means that the high bioactivity in the honey affects the results of a test used to detect fraudulently added cane sugar. Karyne led a joint honey study with participants from 10 international honey testing laboratories to examine the testing issues.

Her research has led to the acceptance of new test criteria to accommodate New Zealand honey that was giving false-positive test results

Karyne says that the test itself remains the same, but the interpretation of unusual varieties of honey such as manuka has been changed slightly. Its carbon isotope value is now the main indicator of purity rather than its ‘apparent’ cane sugar level.

A recent consumer survey of manuka honey in Hong Kong has also raised some issues surrounding testing of 55 manuka honey samples, in which 14 exceeded the allowable level of sugar addition.

To be acceptable to importing countries, honey must have a cane sugar content below 7 percent by volume. The flawed method was not measuring the real cane sugar content, and gave only an ‘apparent’ value.

The new criteria allows atypical honey, such as manuka, to have slightly higher cane sugar levels as long as its carbon isotope value is within a certain limit.

Prior to 2010, New Zealand honey products were not routinely tested on arrival in destination countries. However, overseas countries became more vigilant with testing in 2010 in the wake of a sharp increase in honey fraud originating from Asia.

Asian countries were selling inferior sugar-adulterated honey, some of which contained harmful residues and antibiotics, into premium markets worldwide. The increased testing was useful to detect issues with Asian honey, but also found that New Zealand manuka honey was prone to fail the cane sugar test.

As a result of test failures in the past three years, bee keepers have been either holding onto their high-value bioactive manuka honey, or blending it with lower activity manuka containing a lower sugar content to bring down its ‘apparent’ cane sugar levels.

Changing the test criteria will free up about $40 million of export manuka honey, which previously did not meet the standard laboratory test.

Karyne Rogers and her team have found that Manuka honey often has higher levels of pollen compared to other honey types. The pollen levels are artificially high because of the intensive extraction method used for Manuka honey .

Dr. Rogers found that pollen contained in Manuka honey had a different isotopic value to the protein. The unmodified testing regime isolates the protein from the honey for comparison testing, but the current protein isolation method does not remove the pollen beforehand.

Protein isolated from Manuka honey with high pollen counts ended up with the pollen contaminating the protein isotopic value – giving a false positive result for added C4 sugars and failing the test.

When the pollen was removed before the protein extraction, the honey passed the test. Dr Rogers has shown that a true comparison can now be made between the whole honey and the protein.

The key advantage of the modification will still pick up sugar adulteration at the same time as reducing or removing the false positives.

During winter feeding, sugar can be a way of ensuring hives survive the winter. It can also help with pollination of low nectar crops like kiwifruit. Beekeepers routinely feed sugar to their hives during kiwifruit pollination. However this cane sugar can contaminate and affect the purity of the honey.

To prevent rejection of honey, Karyne Rogers recommends that any producer who sugar feeds their bees should submit their honey for isotope testing. She adds “blending a batch of honey collected too early from C4 sugar fed bees can contaminate an entire shipment”. To avoid costly mistakes, producers should test each batch to eliminate any questionable batches from the main harvest. Testing will also help producers to understand withholding periods of sugar before collection occurs, to minimise the risk of a failed test. Other solutions to this problem could include the removal of brood boxes from the collection boxes or wintering bees using natural products such as honey.